1. Field of the Invention
This invention generally relates to a safety arrangement for and a method of protecting workers from injury while working on an elevated structure such as a railway bridge, as well as to a method of installing such an arrangement.
2. Description of Related Art
It was known from my U.S. Pat. Nos. 3,949,834; 4,838,382 and 4,856,615, and from my pending allowed U.S. patent application Ser. No. 07/784,559 filed Oct. 29, 1991, to erect safety nets adjacent an outer face of a building under construction in order to catch workers and/or objects falling off a floor above the net, thereby protecting the fallen worker, workers on lower floors, as well as passersby at ground level, from being injured. It was also known from my pending allowed U.S. patent application Ser. No. 07/789,660 filed Nov. 8, 1991, to suspend a safety net across an open elevator shaft for catching workers and/or objects falling down the elevator shaft in a multi-floor building under construction.
A common feature of those known safety net arrangements was that the nets were supported by net supports which were anchored on the building under construction. A plurality of anchor holes were formed at the periphery of one or more floors of the building, and floor brackets were anchored to the floor by anchor bolts positioned in the various anchor holes. The formation of such anchor holes, the mounting of anchor bolts therein, and the eventual removal of the anchor bolts from the anchor holes during building construction was a labor-intensive and expensive task.
During the maintenance, repair or construction of such elevated structures as a bridge, particularly a railway trestle bridge, at a considerable height off the ground, it was known to protect workers from injury by suspending nets outwardly of the bridge. Such a railway bridge included at least one pair of parallel steel I-beams for supporting railway ties on which a pair of rails were supported. Each I-beam included a web and a pair of upper and lower flanges integral therewith. Even though each I-beam had considerable inherent strength and, for example, each web might be on the order of one meter high, it was conventional to weld L-shaped stiffeners at various locations on and along the web to prevent buckling due to the weight of passing railroad cars, especially loaded freight cars. The aforementioned known bridge nets were supported by net supports from the I-beams. These net supports were anchored in anchor holes which were either drilled into the web itself or, preferably, into the stiffeners. In either event, the physical integrity and strength of the supporting I-beams were weakened. Sometimes the stiffeners were pre-drilled with holes, but this was for the purpose of accommodating the routing of communication and/or power electrical cables underneath the bridge. If the electrical cables were not in place, then the net supports could be fastened by anchor bolts using the pre-drilled holes in the stiffeners. However, it was more frequently the case that the pre-drilled holes were used for their intended cable-routing purpose, and there simply were no holes available to receive anchor bolts to which the net supports could be attached. As in the case of installing safety nets on buildings under construction, the formation of such anchor holes in the I-beams, the mounting of anchor bolts therein, and the eventual removal of anchor bolts therefrom was a labor-intensive task and was all the more difficult in the case of a railway trestle bridge. It was far easier to form holes at the periphery of a building floor under construction where access and power tools were readily available, as compared to the case of forming anchor holes in an I-beam located underneath the railway ties.